The Taoiseach has not dismissed the idea of building a bridge between the North and Scotland, but insisted the UK must pay for it.
British Prime Minister Boris Johnson and the DUP have spoken in favour of the idea.
Last week Mr Johnson described it as a “very interesting idea”, adding: “Watch this space.”
Leo Varadkar said he had discussed the idea with the Prime Minister recently, revealing he told him it was “worth examining”.
But the Taoiseach said he had also told Mr Johnson he would expect the UK to pay for it.
Mr Varadkar said: “At which point he suggested, ‘No, no, the EU is going to pay for it’.
“So that’s definitely not going to happen, because neither Northern Ireland or Scotland are going to be in the EU. But it was kind of half serious, half joking in a way.
“But all messing aside, I do think at the very least a high-level engineering assessment should be done as to whether it is a viable proposal.”
However, Mr Varadkar said he is more interested in talking to Mr Johnson about other projects the two nations could work on together, such as a high-speed rail link connecting Dublin, Belfast and Cork, and better connections to the north-west.
He suggested hourly trains between the cities as well as improving the A5 road to Derry and Donegal.
Mr Varadkar said he was also interested in the idea of a cross-border university, involving the Ulster University campus at Magee in Derry with Letterkenny IT, as well as the greenway projects and the Ulster Canal.
